This probably falls under the category where you suggest that your client verify what ID belongs in the box with their tax advisor, but maybe the following will help explain what's going on. As an Arizona employer, I make payroll withholding deposits in Arizona. When I report those deposits in the AZ DOR (Dept of Revenue) website, the Taxpayer EIN I use is my Federal ID. So it sort of follows that all the state W-2s should tie back to that. Although I have separate state IDs for Sales tax and Unemployment Insurance, the AZ DOR website does not use those for W-2 related filings. So I guess I am saying that it is probably not a software malfunction, but they should call their tax people to verify the correct ID to use. I believe we used to report using separate FED and AZ EINs, but not currently.